Field
The invention relates to an over-the-air testing of a device in an anechoic chamber.
Description of the Related Art
When a radio frequency signal is transmitted from a transmitter to a receiver, the signal propagates in a radio channel along one or more paths having different angles of arrivals, signal delays and powers, which causes fadings of different durations and strengths in the received signal. In addition, noise and interference caused by other transmitters interfere with the radio connection.
A transmitter and a receiver can be tested using a radio channel emulator emulating real circumstances. In a digital radio channel emulator, a channel is usually modeled with a FIR filter (Finite Impulse Response filter), which generates convolution between the channel model and an applied signal by weighting the signal, delayed by different delays, with channel coefficients, i.e. tap coefficients, and by summing the weighted signal components. The channel coefficients are functions of time to correspond to the temporal behavior of a real channel. A traditional radio channel emulator test is performed via a conducted connection such that a transmitter and a receiver are coupled together via a cable.
Communication between a subscriber terminal and a base station of a radio system can be tested using an OTA (Over The Air) test where a real subscriber terminal is surrounded by a plurality of antennas of an emulator in an anechoic chamber. The emulator which may be coupled to or act as a base station emulating paths between the subscriber terminal and the base station according to a channel model. In the test, the direction of a path depends on the direction of an antenna, and hence the directions of paths are limited and there is a need for a better OTA test solution.